package/cdrkit: fix static build with libmagic

package/cdrkit: fix static build with libmagic

libmagic is an optional dependency of gensoimage that can raise the
following build failure:

/home/buildroot/autobuild/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/8.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: /home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libmagic.a(compress.o): in function `uncompressbuf':
compress.c:(.text+0x7bc): undefined reference to `lzma_auto_decoder'
/home/buildroot/autobuild/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/8.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: compress.c:(.text+0x828): undefined reference to `lzma_code'
/home/buildroot/autobuild/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/8.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: compress.c:(.text+0x848): undefined reference to `lzma_end'
collect2: error: ld returned 1 exit status
genisoimage/CMakeFiles/genisoimage.dir/build.make:628: recipe for target 'genisoimage/genisoimage' failed

Fixes:
 - http://autobuild.buildroot.org/results/7e06edc363817c9c9a1687ec89e9984a90a2012d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>